Capacity control for steam generators



l Aug. 29, 1950 J. v. PYLE CAPACITY CONTROL Foa STEAM CENERATCRS Filed Jan. 9, 1948 Patented ug. 29, 1950 CAPACITY CONTROL FOR STEAM GENERATORS John V. Pyle, Briar Clil Manor, N. Y., assigner to Kennedy-Van Salm Mfg. & Eng. Corp., New York, N. Y., a corporation of Delaware Application January 9, 1948, Serial No. 1,437

8 Claims. (C1. 236-26) My invention relates to improvements in controlling the capacity of steam generators, and to a pressure operated control which cooperates in a particular manner with the upper and lower portions of a steam generating unit.

One of the problems encountered in connection with steam generating units which include furnaces having water cooled walls is that tube failures have occurred in such walls. Various theories have been advanced for the cause of furnace tube failures in steam generators, Furthermore, these failures result in very high losses not only from the damage done to the plant but also because of the shut-down time and repairs necessary. Insurance claims of many kinds also arise.

In cases Where furnace tubes have failed in large steam generator furnaces, and insurance claims have been led and paid, the damaged plant is usually inspected along with its records. Such records almost invariably show that the water level in the steam and water drum was at normal when the tube failure occurred, thus indicating that there was no lack of water in the unit or negligence in supplying water thereto.

Steam generating units of the type in question have a furnace structure which includes vertical Wall tubes terminating at the top and bottom in headers, the upper of which discharge through connecting tubes into a steam and water drum at the top of the unit. The lower headers are supplied with water by tubes connected thereto from a drum in the lower part of the furnace which in turn is supplied with water by downcomers from the steam and water drum. The tubes between the lower drum or header and the lower headers for the wall tubes are known as feeder tubes, and according to standard practice one feeder tube is provided to supply water for from five to ten wall tubes in the furnace. It is generally believed that the high velocity of the steam and bubbles in the wall tubes `applies a suction to the feeder tubes so as to draw water into the wall tubes and keep them continuously supplied.

With furnaces of the type referred to, it is generally the practice, if possible, to keep the capacity as high as possible, but it will b-e apparent that even though the operator has a water level gauge on the steam and water drum, and knows that he has a normal water level therein, he still does not know and has no means for determining when steaming capacity of the furnace tubes has been reached. According to my understanding of the problemsdiscussed above, a point is reached in the operation where the capacity to supply water to the lower portion of the steaming tubes is exceeded and that consequently some of the tubes which are starved of water become so hot that they fail. It should be understood that the temperatures generated in the combustion chambers of such steam generating units run in the neighborhood of from 2300* to 2700" F.

My understanding of the tube failures in steam generators of this type and the reason why tubes fail in the furnace chamber, is that inmost, if not all cases, the failure is due to operating the unit above safe steaming capacity of the wall tubes of the furnace combustion chamber, at least some of them. While with present equipment it is almost impossible to determine when the limit of steaming capa-city is reached it is my concluson that the tubes in certain places become starved or deprived of sufficient water, because for one reason or another water cannot be supplied fast enough through the headers and feeder tubes provided, at the operating capacity.

The primary object of my invention is therefore to control the unit capacity and provide an improved control which will indicate to the operator the condtion of water supply in the lower headers in the steam generating unit.

In accordance with an important feature of my invention I provide a pressure indicator connected up with the steam and water drum and adapted to indicate the pressure therein. A pressure indicator is also connected up to all of the lower headers in the unit so as 'to indicate the pressures therein. A preferred form of pressure indicator is arranged to show at a glance the difference between the pressure in the steam and water drum and that in a particular lower header of the generator. I also advantageously provide an alarm or signal associated with the pressure indicator which will be operated when the pressure in a lower header approaches within `a predetermined value of that in the steam and water drum.

I advantageously control the operation of a steam generator to avoid starving any `of the furnace tubes, by controlling the firing and capacity of the generator in accordance with a comparison of the pressure in a lower header with that on the generator, and decreasing the firing rate when the pressure in the lower header approaches within a predetermined value of the pressure on the generator.`

In large steam generator installations of the type under consideration, the head. of water which would normally be maintained. in such a unit may be in excess of 30 to 4.0 feet between one oi the lower headers and the water level in the steam and water drum, My improved apparatus is therefore based upon the idea of utilizing the difference in pressure between these points due to the hydrostatic head or" water. When the unit is operated at a normal safe capacity the pressure in the lower header will be greater than that in the steam and water drum by the pressure due to the weight of the column of water. If the operator iinds that the pressure in the lower header begins to approach that in the steam and water drum, he will know the unit is being operated in excess of its safe capacity, even if at the same time his gauge shows plenty of water in the drum. The operator therefore must adjust the unit to bring it out of the danger Zone, for example, by reducing the firing rate.

My invention includes other features and advantages which will be described in greater detail hereinafter in connection with the accompanying drawing forming a part of this application.

In the drawings: Y

Fig. V1 is a vertical broken viewrpartly in section, showing a portion of a steam generating unit in `connection with which my invention is shown and illustrated diagrammatically.

Fig. 2 is a sectional View on an enlarged scale of one of the pressure responsive cylinders shown in Fg. l: i

Referring to the drawings, the steam generator shown includes a portionwof the side wall built in connection with the structural steel members I0, I2 and lei. The unit includes a steam and water drum l at the top of the unit water drum I8 at the bottom, these drums being connected by a pair of downcomer pipes 2t for flow of water from the ends of the drumY it to the ends of the drum I8. The large pipes 2t are outside the furnace or combustion chamber which is indicated at 22. Y

The combustion chamber is denned by a side wall 2d including closely mounted radiation steaming tubes 26 extending between header and 3D. Water is supplied to the header is from the drum I8 through feeder tubes connected into distributed points along the drum 53. Steam and water are discharged from the header :28 into the drum I6 through tubes in the usual manner.

The far end wall of the combustion chamber 22 includes closely mounted radiation steaming tubes 36 extending between headers 3S and Water is supplied from the drum I8 to the header 38 through spaced groups of feeder tubes ft2, while steam and water flow from the header Il@ into the drum IB through tubes M.

In the particular generator unit illustrated, a tube wall is provided at the near end of the 'combustion chamber 22 by installing a row of radiation wall tubes d@ extending directly between drums I and I8. The tubes 126 at the lower portion of this tube wall are bent out of alignment in a conventional manner so that combustion gases produced in the combustion chamber '22 pass through the lower portion of the wall to Contact superheater and economiaer tube banks (not shown) in a known manner. In the generator structure as shown, the headers 23, Sil, and 4i] and the ends of the tubes connected thereinto are covered in the combustion chamber by fire brick or other refractory material lil, as indicated.

The steam and water drum it is provided with a liquid level gauge 48 and in accordance with cated by the hand li.

the features of my invention, this drum is connected by a line 553 to a pressure gauge or indicator 52. The liiie 50 connects into the steam space of the steam and water drum I6 so that the normal pressure maintained on the generator is transmitted through the line 5e to the pressure gauge or indicator 52. Wa r is supplied to the generator in accordance with the usual practice and introduced, preferably in a preheated state, into the steam and water drum l to maintain the desired water level therein, as indicated by the gauge A8. The instrument 52 may be located above the generator to provide drainage in the line 5d.

The pressure gauge 2 comprises part of the mechanism for controlling the capacity of the generator and for preventing the blowout of radiant wall tubes in the combustion chamber. The mechanism shown is merely diagrammatic, and the means shown for indicating the pressure in the steam spaceV of the steam and water drum i5 includes a pointer or hand 54, a scale lit` and an operating cylinder 58. The hand 513 is pivoted on a shaft 59 and includes a pinion hub 66 operated by a rack E52, as shown more .in detail in Fig. 2. In this view the pressure medium acting in the line 5l) operates against a spring-loaded piston 64 in the cylinder Y58. n Therack 52 is connected in the manner shown to the piston B, so that any variations in the pressure in the vline 5t will eiect movement of the hand '54 with respect to the scale 55u/nichv is calibrated to indicate the pressures in pounds per square inch in the generator.

The gauge or indicator 52 includes another pressure indicator hand 66, a part of which is made of insulating material and shown in black. This hand has a pinion hub which is pivoted on the shaft 5S. The hub 68 is operated )by a pressure cylinder arrangement lll like that shown in Fig. 2. A pressure line 'I2 connects into the cylinder and is in turn connected into branch lines I4, 'i6 and i8, having valves '15, Tl and i9, which are respectively connected into headers 38 and Sil and water drum i8. Since the pressure line l2 connects into the lower part of the unit and a substantial head of water is normally maintained therein, the pressure indicated by the hand @twill be substantially above that indi- Provision is made for selectively connecting up headers 3B, 38 and water drum i8, and it will be understood that the pressure as registered when these different levels in the generator are connected up, will be diiierent, due to the differences between the heights of the water columns involved.

The indicator 52 is advantageously connected up to an alarm or a generator control, or both. Accordingly, in the illustrated embodiment, the hand 5ft is provided with a contact member 8E) while the Vhand 55S has a similar contact member 82. The member is connected through a wire 8d, to an alarm 8S, illustrated as a gong or bell, while the member B2 is connected by a wire 88 to a battery 90, which in turn is connected to the alarm 86. Wires 92 also connect upa control Qd with the contact members 8E) and B2. through wires 84 and 88, and wires 9F: lead to a motor or other control mechanism 98 for the steam generator, which is particularly adapted to reduce its capacity or output, such as combustion control. The control mechanism 9B, for

example, may operate a control valve |00 in aV fuel supply duct |92 leading to the generatorV burners (not shown) the `operation of .gradually increased, either one of the headers 3U or 38 may be` first to be starved of water. The

lines I4 and 'I6 may be selectively cut intothe line 'I2 at different ratings to obtain an indication by the position of the hand 66 with respect to the hand 54. The nearer the hand 66 approaches the hand 54, the lower`the water supply t() the particular header., @The hand E5 is mounted slightly in front of the hand 54 andthe contacts 8G and 82 are `'advantageously arranged so that when the hand 66 approaches to within a predetermined distance or pressure, for example ve pounds of the pressure shown by the hand 54, for a generator of the size described, the contact 82 will engage the contact Bil and set oiithe alarm 8B, and, if desired, put in operation the capacity reducing control 94. The instrument may include a hand for each lower header and for drum I8.

Since the water supplied to the headers 30, 38, and others in the lower portion of the generator must come from the water drum I8, a small movement of the hand 66 toward the hand 5t from its normal spacing therefrom, when the drum I8 is connected up, will indicate an approaching more serious water shortage in the headers 3D, 38 and others supplied by the drum I8. Therefore, the instrument 52, may, if desired, include a special indicating hand which is separately connected up to the drum I8 and which would give a signal or actuate the control 94, or both. However, if a slight shortage of water, accompanied by a lower pressure in the drum I8, should occur, there would be at almost the same time, a more serious shortage in the headers 30, 38, and others in the lower part of the generator. The indicator, therefore, will in most cases, give proper protection if connected into one of these headers.

After trial runs on a generator with the indicator apparatus installed, the operator will know which header or headers rst become starved of water as the output of the generator is increased. Such header or headers may thereafter be kept continuously connected into the pressure line 12.

It will be understood that the examples described above are merely illustrative and that the apparatus is diagrammatic. The pressure piping for the indicator 52 may include a sealed hydraulic system which has branch lines responsive respectively to the pressure in the drum I8 and in the headers in the lower part of the generator, while another line, 5I), is responsive to the steam pressure in the drum I6.

What I claim is:

1. In an apparatus for controlling the capacity of steam generators having combustion chamber walls which include long bare radiation steaming tubes connected into headers in the lower portion of the generator and from the upper ends of which steam and water are conducted into a steam and water drum, a water level gauge on the steam and water drum, and means for conducting water from the steam and water drum into the headers, the improvement for preventing starving of the tubes and headers for water when an ample supply of water is present in the :sure 'responsive mechanism connected by' acoii duit into the `steam andwater drum `and having a movable indicator member responsivetolthe pressure in the steam and water'drum and which indicates the pressure therein, said mechanism 'also being connected by a conduit into a header 4 in the lower portion of the generator and having a second movable indicator member whicl'iis responsive to the pressure in the headerand which indicates the pressure in the-said header, a `controlcircuit forcontrolling the generator and having separatemeans connected. respectively to said members, and means responsive to the movement ofthe second movable meinber'- to `a sure of that indicated by the rstmovablemember for energizing-the control circuit, whereby the `generator is maintained atl` a` sate steaming capacity with-an ample water supply for :the steaming-` tubes.` i J 2.` An apparatus asidenedby claim 1 in which the control circuit includes an alarm for indieating that steaming tubes are being starved for water.

3. In an apparatus for controlling the capacity of steam generators having combustion chamber walls which include bare radiation steaming tubes connected into headers in the lower portion of the generator and from the upper ends of which steam and Water are conducted into a steam and water drum, a water drum in the lower portion of the generator, and means for conducting water from the steam and water drum into the water drum and from there into the headers, the improvement for preventing starving of the tubes and headers for water when an ample supply of water is present in the steam and water drum which comprises a pressure responsive mechanism connected by a conduit into the steam and water drum and having a movable member responsive to the pressure maintained therein, said mechanism also being connected by a separate conduit into a header in the lower portion of the generator and having a second movable member adjacent the rst which is responsive to the pressure in the said header, a control circuit for controlling the generator and having separate means connected respectively to said members, and means responsive to the movement of the second movable member toward the rst to a predetermined extent for energizing the control circuit, whereby the generator is maintained at a safe steaming capacity and starving of the tubes for water is prevented.

4. A generator as defined by claim 3 in which the control circuit includes an alarm to warn of an approaching lack of water in said header.

5. An apparatus as defined by claim 3 in which said circuit includes a generator capacity reducing control adapted to be energized in response to a pressure drop in said header below a predetermined normal pressure with respect to that in the steam and water drum.

6. An apparatus as dened by claim 3 in which means is provided for selectively connecting said mechanism into a plurality of the headers in the lower part of the generator.

'7. In an apparatus for controlling the capacity of large steam generators having combustion chamber walls which include long'upright bare radiation steaming tubes connected into headers in the lower portion of the generator and from the upper ends of which steam and water are conducted into a steam and water drum substeam and water drum which comprises a, presstantally above the headers, and means for conateo-,51p

ducting Water from. the steam and water drum through a downccmer and into the' headers, the improvement for Y preventing starving of the Y tubes and headers for water when an ample supply of water is present in the steam and water drum which comprises a pressure responsive mechanism connected by a conduit into the upper portion of the steam and water drum and having a movable member responsive to and which is arranged to indicate the normal pressure therein, means including a conduit connecting saidmechanism into a header in the lower portion of the generator, said mechanism having a second movable member which is responsive to and which is arranged to indicate the pressure in the said header, a control for the generator, and means connected to said control and responsive to the movement of the second movable member to a predetermined pressure lower than its normal pressure with respect to theY normal pressure indicated by the rst mov- 8 ableVv member `for energizing the control whereby the generator is maintained 'at a safe steaming capacity for preventing starvation of the header for water when ample water is present in the steam and water drum;

8'. A-n apparatus als claimed in claim 1 in which said control circuit includes an electrical circuit, ari electrical cntact carried yby said members in opposed relation,'and wires respectively connecting said contacts into the electrical circuit.

JOHN V. PYLE.

REFERENCES CITED The following" references are of record in the -l of this patent:

NTE STATES PATENTS 

